1. Field of the Invention
This invention relates to greases and more particularly, to greases which contain a calcium or calcium/lead complex thickener.
2. Description of the Prior Art
Calcium soaps have been used for a long time as grease thickeners. For example, J. I. Clower referred to the use of lime base greases in "Lubricants and Lubrication", First Edition, McGraw-Hill, New York 1939, page 68 et seq. The soaps are produced by the saponification of fatty materials (naturally occurring triglyceride esters or the fatty acids derived from the glycerides) with lime, as is conventional in the art. The use of various complex soap thickeners such as the mixed calcium salts and soaps is also known. For example, Boner in "Manufacture and Application of Lubricating Greases", Krieger, 1971 (reprint of 1954 edition), Chapter 16 refers extensively to such complex soap thickeners and Liddy U.S. Pat. No. 2,999,065 discloses the use of calcium complex thickeners derived from low, intermediate and high molecular weight acids. Schott U.S. Pat. No. 2,898,297 describes a calcium complex thickener which includes calcium soaps derived from nut oil acids.
The lubricating vehicle base stocks which have been used with these thickeners have been naphthenic in nature. That is, the hydrocarbons in the base stock have been predominantly alicyclic rather than straight chain. These base stocks have been preferred because they give a firm-bodied grease whereas paraffinic base stocks yield soft-bodied greases with the same amount of a given soap thickener. Thus, the naphthenic base stocks give a better yield of grease in relation to the amount of thickener. Although it would be possible to use a greater amount of thickener to produce a grease of given consistency using a paraffinic base stock, the high cost of soap relative to that of the oil has generally made this uneconomical. In addition the amount of soap necessary to produce a thick bodied base with a paraffinic base, e.g. NLGI Grade 3, can lead to an unstable grease structure. Such a grease might soften during use (as a result of which it might run out of the bearings in which it was being used).
U.S. Pat. No. 3,705,853 to Fau describes the use of certain ethylene terpolymers as improvers in calcium and calcium/lead thickened greases.